The present invention relates to a magnetic head and its manufacturing method and, particularly, to a magnetic head comprising a magneto resistance effect device as a reproduction device and its manufacturing method.
A magnetic recording and reproduction device records information by the magnetization direction of a medium and reproduces the information as voltage. This device comprises a medium for storing magnetization information, a recording head for generating a magnetic field to record information, a reproduction head for reading information on the magnetization of the medium, a mechanism for driving these heads and the medium, a recording and reproduction operation control circuit for controlling these, etc. The magnetic head is designed to float above the medium at a fixed height during its operation. A so-called “spin valve structure” which has two or more magnetic layers and obtains an output voltage from the relative angle of magnetization between them is widely used for the reproduction head.
Along with an increase in the density of a magnetic recording device, the minimum unit for recording information, that is, the size of recording bits is becoming smaller and smaller. To reduce the number of recording bits, the bit length and the track width must be reduced. To reproduce information from fine recording bits at the time of reading information, it is desired that a magnetic flux from the bits of interest should be detected with the reproduction head at high sensitivity whereas a magnetic flux from other portion which is the cause of a noise should not be detected as much as possible. Therefore, an upper shield and a lower shield composed of a soft magnet, e.g., Ni—Fe alloy in most cases are formed above and below the reproduction head in the bit length direction. The upper shield and the lower shield absorb a magnetic flux from an unnecessary area to contribute to the reduction of the influence of a sensor portion with respect to the bit length direction of a recording bit to be reproduced. It is thus known that the shields composed of a soft magnet have an effect in the bit length direction.
In recent years, a CPP (Current Perpendicular to the Plane) system in which a sense current is applied perpendicular to the film plane has been attracting much attention. According to this system, compared with the conventional CIP (Current In the Plane system that a sense current is applied in the plane direction), an insulating layer does not need to be formed between the upper shield and the lower shield, thereby making it possible to reduce the distance between the upper shield and the lower shield. Accordingly, it is considered that the CPP system can improve resolution in the bit length direction.
In the so-called “spin valve type” reproduction head, a magnetic field (so called “longitudinal bias”) must be applied in the track width direction in order to suppress a noise caused by a free layer. There has been generally employed a so-called “hard bias system” that a longitudinal bias magnetic field is generated by a ferromagnet arranged on right and left sides of a sensor. Since the magnet used for the hard bias desirably generates a magnetic field in the same direction without being disturbed by an external magnetic field, a hard magnet is used. Meanwhile, the shields are desired to have soft magnetic properties. Since the hard bias and the shields differ from each other in required magnetic properties, when a hard bias system is used in combination, it is difficult to arrange a soft magnet on the right and left sides of the sensor and a magnetic shield effect cannot be obtained in the track width direction. Therefore, a phenomenon (so called “side reading”) where information is read from the adjacent or nearby track occurs in the reproduction track width direction.
As means of providing a longitudinal bias magnetic field to the free layer, there has been proposed a system making use of magnetic interaction from the longitudinal bias layer formed above or below the sensor and not the ferromagnet arranged on the right and left sides of the sensor. For example, Journal of Applied Physics, vol. 93, No. 10, pp. 7310-7312 shows that a structure consisting of a soft magnet and an anti-ferromagnet is used as a longitudinal bias layer. Besides the structure consisting of a soft magnet and an anti-ferromagnet, a system using an anti-ferromagnet is also shown in Journal of Applied Physics, vol. 89, No. 11, pp. 7359-7631.
When this biasing system is used, it is not necessary to arrange a ferromagnet on the right and left sides of the sensor and accordingly, it is possible to arrange a soft magnet on the right and left sides of the sensor in place of the ferromagnet. For example, JP-A 2003-264324 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) shows the effect of reducing the effective track width by arranging a soft magnet on the right and left sides of a sensor (so-called “side shield effect”). However, these documents do not mention the shape of the soft magnet (side shield) arranged on the right and left sides of the sensor and the shape of the sensor itself.
The side shield must efficiently absorb a magnetic flux other than a signal of interest generated from the adjacent track on the medium and so on. At the same time, a magnetic flux must not leak to the sensor side from the side shield. However, as will be described hereinafter, according to computer simulation conducted by the inventors of the present invention, it was found that a magnetic pole is generated on a side next to the sensor of the side shield according to the shape of the side shield. As this magnetic pole changes by the movement of magnetization in the side shield, it can be the cause of a noise to a reproduction signal. Even when the generated magnetic pole does not change, it is possible that magnetization rotation in the free layer may be prevented.
JP-A 264324/2003 discloses a diagram showing that the angle formed by the film plane of the sensor and the side shield is about 65° as an embodiment of that invention. It is further illustrated that the angle formed by the side face of the sensor itself and the film plane of the sensor is also about 65°. That is, in that invention, the plane of the side shield and the side face of the sensor are parallel to each other and it is not taken into consideration to control the shape of an insulator sandwiched between them. Similarly, U.S. Pat. No. 6,680,832 discloses an example in which the angle formed by the film plane of a sensor and the side shield is 90° but does not mention the control of its shape. U.S. Pat. No. 6,680,829 discloses a structure that a soft magnet is arranged on the right and left sides of a sensor but both ends of the sensor are composed of a conductor and the sensor has a CIP structure. That invention is characterized in that a soft magnet arranged as a side shield also serves as an electrode and that the side shield is insulated from the upper shield and the lower shield. It is not mentioned in that invention that characteristic properties are improved by changing the shape of the side shield.